Networks having different characteristics may be integrated for the purpose of simplifying information system operations and management and the like. Hereinbelow, a network constructed by integrating a plurality of networks is called an integrated network.
Recently, the integration of, for example, local area networks (LANs) and storage area networks (SANs) is being carried out. However, there is a problem in that the fundamental technology may be different when integrating a LAN and a SAN. For example, the standard specification used in a LAN is Ethernet (trademark), while the standard specification used in a SAN is Fibre Channel. Thus when integrating a LAN and a SAN, technologies such as Fibre Channel over Ethernet (FCoE) or data center bridging (DCB) are used.
Multiple types of communications with differing allowance rates for dropped frames may be conducted in an integrated network built by the integration of a LAN and a SAN. For example, a characteristic of FCoE is that storage access performance drops dramatically when frames are dropped. Although the dropping of frames is allowed to some extent in video and audio streaming, FCoE exhibits poor quality due to breaks in video and audio streams when the dropping of frames becomes noticeable. Moreover, a transmission control protocol (TCP) used when communicating between servers includes a mechanism to conduct re-transmission when frames are dropped.
Conventionally, flow control using a pause frame is known as a technique to reduce the dropping of frames in a relay device. In this technology, when a utilization amount of a buffer in a network switch approaches its upper limit and there is a possibility that the dropping of frames may occur if more frames are received, a pause frame is transmitted to the frame transmission source to cause the transmission of frames to be suspended. However, this technique has a problem in that to suspend the transmission to each port by the transmitting devices, the transmission of frames that are allowed to be dropped is also suspended.
Meanwhile, in priority-based flow control (PFC) prescribed in DCB, only the frame transmission of communication types (also called flows) prone to frame dropping may be suspended to conduct flow control for each of eight types of priorities prescribed in Ethernet. However, frequently only the transmission of specified flows is suspended when this type of simple control is conducted.
A conventional technique of determining a transmission suspension time for each port also exists in relation to flow control. However, flow control may not be conducted appropriately since the criteria for determining whether or not to conduct the flow control are simple.
A conventional technique called early packet drop (EPD) also exists in which buffer usage limits are provided for each flow to discard frames when the limit is exceeded. According to this technique, the condition of blocking bandwidth control (namely, head-of-line (HOL) blocking) due to frames of specified flows occupying a buffer and blocking the passage of frames from other flows, for example weighted round robin (WRR) or enhanced transmission selection (ETS), is avoided.
However in EPD, it is difficult to balance both reducing the overflow of buffers and securing bandwidth without appropriately setting a threshold for discarding frames. For example, if the threshold is too high the buffers may overflow, and if the threshold is too low, the discarding of frames for flows in which EPD is enabled may occur very easily, and thus a noticeable drop in performance may arise.
There is a technique for monitoring the use of a shared buffer and determining a threshold based on the utilization amount of the buffer at a time when a frame arrives in relation to EPD. However, proper control may not be conducted with this type of technique. For example, when there is a flow without congestion of communication but the utilization amount is high, the threshold may be lowered even though normally the threshold does not have to be lowered.
Another conventional technique includes a spool memory provided between a transmitting buffer and a receiving buffer and the number of buffers in the spool memory assigned to ports is determined according to communication conditions (buffer utilization rate) of the ports. However, the same types of problems as described above occur with this technique since the number of assigned buffers is determined according to the buffer utilization rate at a predetermined point in time.
There is also a technique that predicts future increases and decreases in the number of packets in a buffer based on increases and decreases in the number of packets in the buffer and uses the predicted value to determine a threshold to detect buffer overflows. However, this technique may not be applied to bandwidth control based on WRR, ETS and the like.
The above techniques are discussed in Japanese Laid-open Patent Publication No. 2000-209250, Japanese National Publication of International Patent Application No. 2000-510308, Japanese Laid-open Patent Publication No. 2008-271017, and Japanese Laid-open Patent Publication No. 2004-104192.